Photo: Hunley submarine immersed in refrigerated storage tank at the WLCC upon recovery. Note the cathodic connection to the sub at the spar attachment and the titanium anodes in the white pipes along the submarine.

The Hunley was less than twenty feet away from her torpedo when it exploded, according to new evidence uncovered by experts working to preserve the world’s first successful combat submarine. This is one of the most important clues found to date for archaeologists trying to discover why the Hunley vanished.

Remnants of the torpedo that sank the USS Housatonic in 1864 were found securely bolted to the tip of the spar, a large pole that served as the Hunley’s weapon delivery system. The metal is jagged and peeled away from the aftermath of the explosion. It would have clearly created a risky situation for the Hunley’s crew if the torpedo stayed attached to the spar when it exploded.

“There is overwhelming evidence to indicate this was not a suicide mission. The crew no doubt knew the dangers facing them, but still, they hoped to make it back home. They must have believed this was a safe enough distance to escape any harm,” said Hunley Commissioner Lieutenant Governor Glenn McConnell. “If so, they were at least partially right. Thus far, no damage has been found on the actual submarine caused by the explosion.”

Plan of Attack: The new find is turning upside down the traditional understanding of how the Hunley’s weapon system functioned. Travelling to the target in a 19th century, hand cranked submarine was challenging enough. But how do you actually get the torpedo in the right spot and then trigger it once you are there? The answer has been sitting quietly in the Hunley lab underneath a brittle layer of concretion coating the spar.

Until now, the conventional wisdom has been the Hunley would ram the spar torpedo into her target and then back away, causing the torpedo to slip off the spar. A rope from the torpedo to the submarine would spool out and detonate once the submarine was at a safe distance. This theory has always had difficulty under scrutiny since it would be very hard to actually lodge the torpedo into the hull of the enemy ship.

Finding a portion of the original torpedo casing has enabled the team to confirm a long held suspicion that it was built and designed by a group associated with Edgar Singer (cousin of the famous sewing machine entrepreneur Isaac Singer). A period diagram housed at the National Archives indicates that this Singer torpedo held 135 pounds of gunpowder and was detonated by a trigger mechanism.

This means the Captain had to position the torpedo while still attached to the spar and trigger it when the time was right. The Hunley’s crew was very strategic in their placement of the torpedo. It was detonated right under the stern to maximize the impact of the explosion and ensure destruction of the large Union ship. The explosion was not an accident. It was the result of careful planning.

Reconstructing the Past: There are dozens of possible theories to explain why the Hunley disappeared after sinking one of the mightiest ships in the Union’s fleet. Scientists have long wanted to digitally test the different scenarios using computer modeling. Until now, they have been missing key pieces of information such as the torpedo strength and the approximate location of the Hunley during the deadly explosion.

With the torpedo charge and size now known from the diagram, understanding where the Hunley was in relation to the Housatonic and the blast that dragged her down to the bottom of the sea becomes a matter of arithmetic. The spar measures approximately 16 feet in length and the torpedo 2 feet, meaning the Hunley was at least 18 feet away from the bomb when it went off.

Now, scientists have the information they need to move forward with computer simulations of the attack, which could prove vital in solving the lingering mystery of why the Hunley did not come home on the fateful night of February, 17th, 1864.

What’s Next: The submarine is covered with a layer of rock, sand and silt – often referred to as concretion – that built up over time while she rested on the ocean floor. The concretion serves as protective coating, but also inhibits the effectiveness of the conservation treatment needed to ensure the Hunley’s survival. Scientists will soon begin peeling away the concretion. “What has been concealed under this layer is anyone’s guess. As we remove it, we’ll be seeing the actual skin of the submarine for the first time. Hopefully, we’ll find many new clues to help us have a deeper understanding of the Hunley’s history,” said Lieutenant Governor McConnell.